Japanese Patent Application Laid-Open No. 2011-193678; Japanese Patent Application Laid-Open No. 2012-135184; Yoshiya Ohnuma, Jun-ichi Itoh, “Circuit Configuration and Control Strategy of single-to-three Phase Power Converter with Active Buffer and Charge Circuit”, The 2010 Annual Meeting of the Institute of Electrical Engineers of Japan, No. 4-057 (2010); Yoshiya Ohnuma, Jun-ichi Itoh, “Experimental Verification of Single Phase to Three Phase Converter Using an Active Buffer circuit with a Charge Circuit”, 2010 IEEJ Industry Applications Society Conference 1-124 (2010); and Yoshiya Ohnuma, Jun-ichi Itoh, “Comparison of Boost Chopper and Active Buffer as Single to Three Phase Converter”, The 2011 Annual Meeting of the Institute of Electrical Engineers of Japan, No. 4-042 (2011) each describe a direct power converter. The direct power converter includes a diode rectifier, an inverter and a charge and discharge circuit.
A single-phase AC voltage is full-wave rectified by the diode rectifier, is thus output to a pair of DC power supply lines (a DC link).
The charge and discharge circuit is provided in the DC link and includes a buffer circuit and a boost circuit. The buffer circuit includes a switch and a capacitor connected in series with each other between the pair of DC power supply lines. The capacitor is discharged by conduction of the switch, thus providing power to the DC link.
The boost circuit boosts a rectified voltage from the diode rectifier to charge the capacitor. The charge and discharge circuit accordingly receives power from the DC link. The inverter receives a DC voltage of the DC link and converts it into an AC voltage to be output.